Welding gun

Abstract

A flange section 12 b protruding in a radial direction of a ball screw shaft 6 a is formed at a lower end portion of the ball screw shaft 6 a , and a protrusion stopper 12 a which abuts on the flange section 12 b to prevent the ball screw shaft 6 a from protruding out of the rod 7 is formed in a hollow section of the rod 7 . On the lower side of the hollow section of the rod 7 , there is formed a retraction stopper 13 a which abuts on a lower end portion 13 b of the ball screw shaft 6 a to limit the retraction of the rod 7.

The invention claimed is: 
     
       1. An electromotive spot welding gun which allows a movable electrode tip to advance to and retreat from a fixed electrode tip, comprising:
 a hollow servo motor including a housing disposed to a gun main body, a stator fixed in the housing, and a hollow rotor rotatably supported by the housing; 
 a rod including the movable electrode tip at one end thereof, formed to be hollow on the other end side, and inserted into the hollow rotor; 
 a ball screw shaft fixed to the hollow rotor, including a thread groove extending in an axial direction, and inserted into a hollow section of the rod; and 
 a nut screwed into the thread groove of the ball screw shaft, and integrally formed with the rod on the other end side, 
 wherein a flange section protruding in a radial direction of the ball screw shaft is formed on the movable electrode tip side of the ball screw shaft, and a protrusion stopper which abuts on the flange section to prevent the ball screw shaft from protruding out of the rod is formed in the hollow section of the rod, 
 wherein a retraction stopper which abuts on an end portion of the ball screw shaft on the moveable electrode side to limit the retraction of the rod is formed on the movable electrode tip on the movable electrode side of the hollow section of the rod, and 
 wherein an opening portion is defined through the one end of the rod, the opening portion communication with the hollow section of the rod.